The present invention is concerned with a control circuit for arc welding components to workpieces, in which a component is placed on to a workpiece by a weld gun and after a welding stroke is lifted from the workpiece in a return stroke by igniting a pre-current arc and is brought up to the workpiece again in a forward stroke during the burning of an interconnected welding arc, in which a sequencing control determines the tripping moments of return stroke and forward stroke as well as of the welding arc and a monitoring voltage is bypassed from the pre-current arc ignited at the welding point.
A circuit of this kind is known from German DE-OS No. 31 30 389. In this circuit a signal from the monitoring voltage tapped off on the pre-current arc is bypassed by means of a voltage discriminator as the monitoring voltage rises above or falls below certain voltage values. In these cases there are unfavourable conditions in the weld area for the welding to be carried out, e.g. a greasy surface, which is indicated by a higher monitoring voltage, or a current bridge in the weld area, which leads to a lowering of the monitoring voltage. If such variations in the monitoring voltage are detected in this known circuit, then the further cycle of the started welding operation can be discontinued and an alarm sounded. No other intervention in the welding operation takes place. If the welding operation is switched off before its completion, then this will produce--most certainly by the action of the pre-current arc--a weld area, which is no longer suitable for subsequent perfect welding. If the weld gun cannot be switched off before the completion of the welding operation on account of the speed of the sequence of the welding operations, then non-perfect welding results, which because of the alarm can then be marked and removed.
Additionally it is known from German DE-OS No. 16 15 517 in an electrical control circuit for welding of weld studs to measure the welding current and to switch the latter off prematurely, if its current intensity falls below or above a specified range.
It is an object of the present invention to even out the welding conditions which vary from weld area to weld area and to obtain perfect welds even in unfavourable conditions.